Steering mechanism

ABSTRACT

A steering mechanism for turning the front wheels of a fourwheel vehicle selectively in either direction to different angular positions relatively to their neutral positions by simple manipulation of a common control element for both wheels. For this purpose each front wheel is supported from a vertically disposed shaft which is mounted for rotation about an axis extending diametrically of the wheel, and each shaft carries a gear. Hydraulic cylinders are mounted for rotation about vertical axes at the opposite sides of the plane symmetry between the wheels, and the projecting ends of their piston rods are pivotally connected; and links are pivotally connected between the pivot connection of said piston rods and arms which extend across and are arranged to turn with another set of gears in mesh with said first mentioned gears. Hydraulic circuit means is provided for selectively retracting one of the two piston rods while maintaining the other one in a projected position, and vice versa. When this occurs, the resultant movement of the pivotal connection between the two piston rods along an arc on the side of the retracted piston rod, causes the links to impart a greater degree of rotation to the gears, and hence to the wheel, on the side of the retracted piston rod than to the gears and hence to the wheel on the opposite side.

United States Patent [72] Inventor LasfloSipos Saratoga, Calif. 21 AppLNo. 797,782 [22] Filed Feb. 10,1969 Patented Apr. 20, 1971 [73] Assignee FMC Corporation San Jose, Calif.

[54] STEERING MECHANISM 11 Claims, 13 Drawing Figs.

[52] U.S.Cl ISO/79.2, 74/89.l6,74/99,91/4l1,280/95 51 lnt.Cl B62d5/l0 FieldofSearch..... ..l/79.2;-

60/(lnquired);91/41l;74/89.16, 99; 280/95, 96,

[56] References Cited UNITED STATES PATENTS 2,429,302 10/1947 Abbe 280/ 3,014,734 12/1961 Swenson... l80/79.2X 3,087,564 4/1963 Quayle /79.2 3,239,025 3/1966 Schreck l80/79.2 3,251,433 5/1966 HintzeetaL. ISO/79.2 3,392,797 7/1968 Gibsonetal 180/79.2X

Primary Examiner-Benjamin Hersh Assistant Examiner-John A. Pekar Att0rneys-F. W. Anderson and C. E. Tripp ABSTRACT: A steering mechanism for turning the front wheels of a four-wheel vehicle selectively in either direction to different angular positions relatively to their neutral positions by simple manipulation of a common control element for both wheels. For this purpose each front wheel is supported from a vertically disposed shaft which is mounted for rotation about an axis extending diametrically of the wheel, and each shaft carries a gear. Hydraulic cylinders are mounted for rotation about vertical axes at the opposite sides of the plane symmetry between the wheels, and the projecting ends of their piston rods are pivotally connected; and links are pivotally connected between the pivot connection of said piston rods and arms which extend across and are arranged to turn with another set of gears in mesh with said first mentioned gears. Hydraulic circuit means is provided for selectively retracting one of the two piston rods while maintaining the other one in a projected position, and vice versa. When this occurs, the resultant movement of the pivotal connection between the two piston rods along an are on the side of the retracted piston rod, causes the links to impart a greater degree of rotation to the gears, and hence to the wheel, on the side of the retracted piston rod than to the gears and hence to the wheel on the opposite side.

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SHEET E OF 9 srnsnrno MECHANISM The present invention relates to the steering mechanism of four-wheeled vehicles, such as the small mobile carriers known as pickup trucks or trolleys which are employed in warehouses for picking selected quantities of goods stored in rows of bins and for transferring the picked goods to designated loading zones where they are transferred onto large trucks for transportation to different markets. Vehicles of this type are described, for instance, in US. Pat. No. 3,379,321 of Stanley M. Weir issued Apr. 23, I968. Such vehicles have to maneuver in narrow lanes formed by and between juxtaposed stacks of superposed storage bins, wherein they may encounter other vehicles of the same type. Thus, though frequently of small horizontal compass and considerable height, they should yet be capable of negotiating sharp comers in a minimum area and with a minimum of effort and skill on the operators part.

It has been found that for turning a four-wheeled vehicle within a minimum space, it is advantageous to set its front wheels to different angular positions relative to the plane of symmetry between the wheels in their neutral positions, i.e., the positions which they assume when the vehicle is to follow a rectilinear course. Depending upon the direction of the intended turn and the intended direction of advance of the vehicle, one front wheel, preferably the one of the side of the intended turn should be turned through a greater angle from its neutral position than the other front wheel, i.e., the one on the side remote from the intended turn. For instance, it has been found advantageous to turn the front wheel on the side of the intended turn about a vertical axis through an angle of about 90 into a position approximately at right angles to its neutral position, and to turn the other front wheel through a substantially lesser angle, such as from 45 to 70 into a position, wherein it slants relative to its initial position in the direction of the intended turn of the vehicle. With the front wheels thus positioned, advance of the vehicle in forward direction causes the vehicle to turn into a position at right angles to its original position within a minimum area; and the same is true, when the direction of advance of the vehicle is reversed while the front wheels are in the above defined positions; the vehicle will turn in the opposite direction within a minimum of space into a position at right angles to its original position, the only difference being that the vehicle will occupy a somewhat different area of the floor space.

It is an object of my invention to provide a steering mechanism that effects a differential setting of the front wheels of a vehicle of the type described in either direction by simple and unsophisticated manipulation of a single steering element.

More particularly, it is an object of my invention to provide a steering mechanism, of the type referred to, for four-wheel vehicles, wherein simple and unsophisticated manipulation of a common steering element or member turns the front wheels of the vehicle differentially into positions wherein their axes intersect at points located in the common axis the rear wheels, the preferred position being one in which one front wheel has described an arc of 90 and the other one an arc of significantly lesser angular width into a position wherein its axis intersects the axis of the first mentioned front wheel in the center point of the rear wheel assembly behind said first mentioned front wheel. With the front wheels in the defined positions, advance of the vehicle, whether in forward or rearward direction, is effective to turn the vehicle into a position at right angles to its original position within a minimum area without dragging any one of the wheels during the turning process. According to the present invention either front wheel can be selectively turned to the 90 position and the direction of turning of the vehicle will then depend upon which direction the drive motor is rotated.

Still another object of the invention is to provide hydraulic circuit means that may be operated by selectively turning a steering wheel in one or the other direction, to retract the projected piston rod of one hydraulic cylinder while maintaining the piston rod of another hydraulic cylinder dependably in projected positions.

These and other objects of my invention will be apparent from the following description of the accompanying drawings which illustrate a preferred embodiment thereof and wherein:

FIG. 1 is a fragmentary perspective of a truck provided with the steering mechanism of my invention viewed from a point in front of the truck;

FIG. 2 is a schematic plan view of the truck, with parts of its superstructure removed to expose its base frame and the components of the steering mechanism supported from said frame;

FIG. 3 is a front elevation of the truck and the mechanical components of its steering mechanism;

FIG. 4A is a fragmentary and partly schematic plan view of the mechanical components of the steering mechanism of my invention in neutral position shown in association with a diagram of an exemplary hydraulic system employed to operate the mechanism;

FIGS. 48 to 4E are plan views similar to FIG. 4A illustrating a sequence of consecutive operational positions of the hydraulic system and the steering mechanism controlled thereby.

FIGS. 5A-5E are schematic plan views of a vehicle with its front wheels adjusted by the steering mechanism of my invention, and illustrate the manner in which the vehicle turns upon forward or rearward operation, respectively, of its drive motor.

The truck or trolley equipped with the steering mechanism of my invention comprises a frame 10 having upright members III that define avertical support for an article elevator and other mechanism in the manner disclosed in said Weir patent. Also the frame 10 has beams 13 supporting an operator's platform 13a that may be selectively raised and lowered, and a converged front end l2 and a rectangular rear end 14 (FIG. 2). Supported from the rear comers of the frame for free rotation independent from each other, are two pairs of wheels I60, 16b and Ida, 18b. The converged front end 12 of the frame carries an upwardly turned, centrally located mounting shelf 20 which is pivotally connected to the center of a transversely extending yoke-shaped beam 22, as indicated at 38. Rotatably held in the opposite ends of said beam 22 are vertically disposed shafts 24a and 24b, and rigidly secured to the downwardly projecting ends of said shafts for rotation therewith are brackets 26 and 28, respectively (FIGS. 1 and 3). Rotatably supported from vertically disposed portions 30 and 31 of said brackets 26 and 28 are the front wheels 32 and 34 of the truck or trolley. Wheel 34 is a freely rotatable wheel, while wheel 32 is driven from a reversible electric motor 35 which is mounted upon the side of the bracket portion 31 opposite to the wheel, and which drives said wheel selectively in either direction through a planetary gear transmission. Due to the pivot connection 38 of yoke 22 at the front end of frame It), all the wheels of the truck maintain at all times ground contact during movement of the truck, and the weight of the frame and the weight of any structure supported upon the frame, including the load carried by the truck during practical use thereof, is evenly distributed over three points of support constituted by the three points of an equilateral triangle defined by the center points of the rear wheel assemblies and the pivot point 33 of the yoke beam 22.

For turning the front wheels 32 and 34 of the truck, when the truck is to be steered into one or the other direction, gears 40a and 40b are fixed to the upwardly projecting ends of shafts 24a and 24b, respectively, for rotation therewith, and said gears 40a and 40b are in mesh with other gears 42a and 42b, respectively, which are rotatably mounted upon the yoke 22 of frame (FIG. 3) and which are preferably of a somewhat larger diameter than gears 40a and 40b. Mounted upon yoke 22 for rotation about vertical axes at either side of, and spaced equal distances from the longitudinal, vertical plane of symmetry X of the truck are two horizontally disposed hydraulic cylinders 44a and 44b having piston rods 45a and 45b projected therefrom. The free ends of said piston rods are pivotally connected as shown at 46. When the piston rods are fully projected, as shown in FIG. 4A, the pivotal connection of the projected ends of said piston rods lies in the aforementioned plane of symmetry. Pivotally supported from the pivotally connected outer ends of the piston rods 45a and 45b by the same pivot 46 that connects the piston rods, are the ends of two adjustable interponents or links 48a and 4811 which are adjustable as by a threaded connected between the center member of the link and its end connectors. The opposite ends of said links are in turn pivotally connected to the projecting ends of two arms 50a and 50b, respectively, that extend diametrically across and are arranged to turn with the gears 42a and 42b. When the piston rods 45a, 45b of the cylinders 44a, 44b are fully projected and their pivot connection 46 lies in the hereinbefore defined plane of symmetry x, the arms 50a, 50b on gears 42a and 42b, respectively, extend parallel to said plane of symmetry. In this position of piston rods 45a, 45b, links 48a, 48b and arms 50a, 50b, the front wheels of the truck are in the positions which they must assume when the truck is intended to follow a linear course (FIGS. 4A and 4E).

When one of the piston rods is retracted, while the other is maintained in projected position, the common pivot connection 46 of piston rods 45a, 45b and links 48a, 48b moves along an arc Y or 2, as the case may be, of a radius equal to the distance between the axis of the pivot connection 46 and the axis A, or A, of rotation of the cylinders 44a, 44b respectively on one or the other side of the plane symmetry X (FIG. 4A), depending upon which one of the piston rods is being retracted and which one remains projected; and when this occurs, the link 48 on the side of the plane of symmetry X into which the pivot connection 46 moves, imparts greater rotation to its gear 42 and hence to the front wheel controlled by said gear than the opposite link. For example FIGS. 4A, 4B and 4C illustrate the sequence of positional changes that occur when the left cylinder 44a is operated to retract its piston rod 45a while the right piston rod 44b is held in its fully projected position. When this occurs, the pivotal connection 46 follows the arc Yon the left side of the plane of symmetry 1: from the position illustrated in FIG. 4A into the positions illustrated in FIGS. 48 and 4C. This causes links 480 and 48b move to the left and as pivot connection 46 moves towards hydraulic cylinder 44a, the links pivot as to straighten out, increasing the included angle between links. Thus, arm 50a is moved to the left by both the leftward and pivoting movement of link 48a. In contrast, arm 50b moves to the left with leftward movement of link 48b but such movement is reduced by the pivoting movement which tends to move that link to the right. As a result thereof, the two gears are turned to significantly different degrees in counterclockwise direction; and when the components of the described actuating mechanism, i.e., the gears 40a, 40b, 42a, 42b, the links 48a, 48b and the hydraulic cylinders 44a, 44b with their piston rods 45a, 45b, are proportioned as shown, full retraction of the piston rod 45a while the opposite piston rod 45b remains in fully projected position, is effective to impart such rotation to the enmeshed gears 42a, 40a as will turn wheel 32 from the forward position illustrated in FIG. 4A through an angle of 90 to the laterally directed position illustrated FIGS. 4C while the other front wheel 34 is turned in the same direction to a substantially lesser degree. If the components of the described steering mechanism are properly proportioned such as illustrated in the drawings, the degree of rotation imparted to the front wheels 32 and 34 about their vertical axes by the described actuation of the steering mechanism, is such that a rearward projection of the axes of rotation of the front wheels intersect at all times in points that lie in the vertical plane of the common axes of rotation of the rear wheels 16a, 16b, 18a, 18b. Hence whatever positions the front wheels assume by actuation of the steering mechanism of the invention, operation of the drive motor, whether in forward or rearward direction, will cause the vehicle to turn about a vertical axis passing through the common axis of the rear wheel assemblies so that there is no possibility for the front wheels to drag during the vehicle turning operation.

When the described steering mechanism has been fully operated, i.e., when the piston rod of the left hydraulic cylinder has been fully retracted, while the piston rod of the right cylinder has remained in fully projected position, such as illustrated in FIG. 4C, the left front wheel 32 has described an arc of about its vertical axis while the right front wheel has made a turn to a position wherein its horizontal axis of rotation R (FIG. 5A) intersects the horizontal axis of rotation Lof the left front wheel in the center point of the left rear wheel assembly. With the front wheels thus positioned, forward operation of the drive motor 35 is effective to turn the vehicle about a vertical axis passing through the center C of the left rear wheel assembly from the initial position shown in thin lines in FIG. 5A to the position T shown in heavy lines in said FIG. wherein it has made a full turn to the left within a minimum of space. On the other hand, operation of the drive motor in reverse position is effective to turn the vehicle to the right about the same vertical axis, i.e., an axis passing through the center point of the left rear wheel assembly, into the position T shown in heavy lines FIG. 58 wherein the vehicle faces to the right, within a differently located area of the same limited size as required for turning when the drive motor is operated in forward direction.

What has above been said with regard the operation of the steering mechanism of my invention for turning the left front wheel of the vehicle from a position parallel to the plane of symmetry of the vehicle into a position at right angles to its initial position, is analogically true for use of the described steering mechanism for turning the right front wheel into a position at right angles to its initial forward position. Full retraction of the right piston rod while maintaining the left piston rod in its fully projected position, is effective in a manner symmetrically identical to the manner described above, to turn the right front wheel of the vehicle from its initial position parallel to the plane of symmetry of the vehicle to a rightwardly directed position at right angles to said initial position as seen in light lines in FIG. 5C, while turning the left front wheel to a significantly lesser degree in the same direction, with the horizontal axes of rotation of both wheels intersecting each other in the center point of the right rear wheel assembly. In this position of the front wheels, activation of the drive motor in forward direction is effective to turn the vehicle within a minimum area about an axis C intersecting the center point of its right rear wheel assembly fully to the right to position T (FIG. 5C), and reverse operation of the motor is effective to turn the vehicle about the same axis, i.e., a vertical axis passing through the center point of its right rear wheel assembly, fully to the left as illustrated in FIG. 5D to position T FIG. 55 illustrates the four positions T ,T,, and particularly indicates the floor area utilized to effect movement of the operator end OE of the vehicle to four distinct positions as well as to move the elevator end EE of the vehicle to said positions.

FIGS. 4A to 4E show schematically an exemplary hydraulic system that may be employed to operate the hydraulic cylinders 44a, 44b in the required manner, i.e., selectively retract the projected piston rod of one while locking the opposite one in fully projected position; and the control member 52 of the system is such that upon manipulation in one or the other direction, it is effective to turn the wheels 32, 34 in the same direction in which it is being manipulated.

Having first reference to FIG. 4A, whenever the steering mechanism of my invention is to be placed into neutral position, i.e., with the front wheels of the vehicle parallel to each other for travel along a rectilinear course, from whatever position the wheels may be at the moment, a so-called centering valve 70 is shifted to the right to deliver the output of an operating pump 71 through a passage 72 and suitable flow lines directly into the piston ends of both the hydraulic cylinders 44a and 44b, i.e., into the spaces of said cylinders between their bottoms and the pistons 73a and 73b, respectively; and another passage 74 of the same valve 70 connects the opposite ends of said cylinders, i.e., the spaces through which the piston rods pass, to the input side of pump 71. With these connections established, operation of the pump 71 is effective to fully project the piston rods of both cylinders as shown in FIG. 4A, and when this position is reached, the centering valve 70 is returned to a centered position, and the piston rods are locked in fully projected condition due to the presence of suitably placed check valves V,, V V and V, in both the fluid supply lines and the fluid escape lines. In FIG. 4A and in the other FIGS. which illustrate schematically different operational positions of the hydraulic circuitry employed to operate the steering mechanism of my invention in the proper manner, i.e., FIGS. 4B to 4E, the active flow lines of the system, i.e., the lines through which fluid passes at a particular operational stage in the performance of the system, and the active control lines, i.e., the lines through which pressure is applied to valves to keep the valves open for return or escape flow, are shown in heavier lines than the idle flow and control lines, and the active flow lines are provided with arrowheads to make it easier to understand the performance of the system.

Connected across the pump 71 in parallel with the centering valve 70 is a valve 75 of the type marketed by Char-Lynn company of Eden Prairie, Minn. under the trade mark Orbitrol. In neutral position, the Orbitrol valve returns fluid recieved from the output side of pump 71 to the input side of said pump (FIG. 4C). It has two ports 76 and 78 which are blocked when the valve is in neutral position. The operation of the valve is controlled by the hereinbefore mentioned control member 52 in the form of a steering wheel, and when the wheel is turned, it directs metered amounts of fluid through one or the other of said ports, depending upon the direction in which the wheel is turned. The amount of fluid delivered through the ports 76 or 78 depends on how much and how often the wheel 52 is turned in the same direction; and when the wheel is turned to open one of its ports for delivery of metered amounts of fluid under pressure through said port, the other port is opened to receive fluid for delivery to the input side of the pump 71.

In the exemplary embodiment of an hydraulic control system for the steering mechanism of my invention illustrated in FIG. 4A to 4E, turning of the steering wheel 52 to the left, i.e., in counterclockwise direction, as viewed in FIG. 4B, is intended to turn the front wheels 32 and 34 of the vehicle to the left. With the centering valve 70 in centered position, the described manipulation of steering wheel 52 directs fluid from the pump 71 through port 78 of the Orbitrol valve 75 to the rod end of the left cylinder 44a and the piston end of the right cylinder 44b, and at the same time the Orbitrol valve prepares a flow passage at 76 for connecting the piston end of the left cylinder and the rod end of the right cylinder through port 76 to the input side of the pump 71. The escape lines for the piston end of the left cylinder and the rod end of the right cylinder join into a common line before they reach the Orbitrol valve, and said common line contains a check valve E2 that nonnally blocks flow of fluid toward the Orbitrol valve. Hence, ordinarily no fluid can escape from the cylinders and their pistons are locked in position. However, the valve 82 may be opened to permit return flow of hydraulic fluid from the cylinders in response to pressure applied through a pressure control line 83 whenever fluid under pressure is delivered to the piston rod end of the left cylinder and the piston end of the right cylinder by the described operation of the Orbitrol valve. Therefore, whenever the Orbitrol valve is in operation to deliver fluid under pressure into the piston rod end of cylinder 44a, valve 82 is opened. The individual escape line from the piston end of the left cylinder, however, includes another check valve 84 which normally opposes return flow of fluid from the piston end of said left cylinder. This check valve pressure line and requires a greater amount of pressure to open it than is required to open check valve 82. Therefore, it is only when the piston rod of the right cylinder 44a has been fully projected, as it has in the positions illustrated-in FIGS. 4A and 4B, and when the operator continues to turn the wheel 52 in counterclockwise direction, that the pressure of the fluid delivered through port 78 of the Orbitrol valve becomes large enough to open check valve 84 to permit escape of the fluid in the piston end of the left cylinder, with resultant commencement of retraction of the piston rod of said left cylinder. It is this check valve arrangement, therefore, which guarantees proper operation of the steering mechanism of the invention in that it insures that retraction of the piston rod of the left cylinder will not commence until and unless the piston rod of the right cylinder is fully projected.

As fluid is forced into the rod end of the left cylinder and the fluid contained in the piston end of said cylinder is allowed to escape, the piston of said left cylinder is being retracted, as shown in FIGS. 48 and 4C. The piston rod of the right cylinder, however, remains in projected condition because fluid under pressure is applied to the piston end of said cylinder and any fluid contained in its rod end was previously ejected. When the piston rod of the left cylinder has reached its extreme position, i.e., is fully retracted, the operator ceases to turn the steering wheel 52 of the Orbitrol valve, causing its ports to be blocked. The left wheel of the vehicle has now turned a full to the left, and its right wheel has turned to a predetermined lesser degree to the left. The supply of fluid under pressure through port 78 of the Orbitrol valve into the hydraulic system ceases, pressure is withdrawn from the valves 82 and 84 in the escape lines from the piston end of the left cylinder and from the rod end of the right cylinder, and said lines are therefore blocked. Check valves 92 and 94 in the fluid supply lines to the rod end of the left cylinder and the piston end of the right cylinder corresponding to the control valves 82 and 84 in the previously mentioned escape lines prevent reverse flow of the fluid supplied to the rod end and the piston end, respectively, of said cylinders. The hydraulic system and hence the steering mechanism of the invention is, therefore, locked in the position illustrated in FIG. 4C and the operator may now safely start the motor 35 of the vehicle in forward or reverse direction as the ,case may be, to turn the vehicle in the manner illustrated in FIGS. 5A-5E.

The wheels are normally restored to their original parallel position by means of the steering wheel. However, if desired, they may be restored to said position by shifting the valve 70 to centered position without manipulating the steering wheel 52 of the Orbitrol valve in any manner. The fluid under pressure delivered through the channel 72 of the centering valve is directed to the piston ends of both cylinders, and the rod ends of both cylinders are connected through channel 74 of the valve to the input side of the pump. Under these conditions the pressure fluid maintains the piston rod of the right cylinder in fully projected position and the pressure fluid delivered to the piston end of the left cylinder moves the piston rod of said cylinder into its fully projected position, since the fluid in the rod end of said cylinder may escape through channel 74 of centering valve to the input side of the pump. Hence the wheels of the vehicle assume the parallel positions for rectilinear travel of the vehicle illustrated in FIG. 4A, and remain locked in this position after the centering valve has been automatically centered, as by spring action in the valve, after the solenoid is deenergized.

Alternatively, the initial parallel position of the front wheels of the vehicle may be restored from the leftwardly turned position shown in FIG. 4C by turning the steering wheel 52 of the Orbitrol valve to the right, i.e., in clockwise direction as indicated in FIG. 4D. When this occurs, metered amounts of fluid under pressure from port 76 are delivered through check valves 82 and 84 to the piston side of the left cylinder and through check valve 82 to the rod side of the right cylinder. At the same time, the check valve 92 in the line between the rod 84 is controlled by pressure applied to it through another 75 side of the left cylinder and port 78 of the Orbitrol valve is opened by pressure applied to it by the fluid emitted from port 76 of the Orbitrol valve through pressure line 93, permitting the rod side of the left cylinder to communicate with the input side of the pump through port 78. Hence, the piston rod of the left cylinder is forced out of the cylinder. The fluid pressure supplied to the hydraulic system by the fluid forced into said system through the left port 76 of the Orbitrol valve, however, is inadequate to open the check valve 94 in the escape line from the piston end of the right cylinder as long as the piston of the left cylinder is still in motion. Therefore. the piston rod of the right cylinder remains locked in projected position until the piston rods of both cylinders are fully projected, as illustrated in H0. 4E. When this occurs, the operator may cease to turn the steering wheel of the Orbitrol valve,.

terminating supply of fluid under pressure through port 76 of the Orbitrol valve, with the result that the front wheels of the truck remain locked in the parallel position for rectilinear travel, since termination of pressure within the system results in closure of all the check valves, 82, 92, 84, 94.

However, if the operator continues to turn the steering wheel 52 of the Orbitrol valve to the right, i.e., in clockwise direction, as indicated in FIG. 4E, the continued supply of fluid under pressure into the system through port 76 of the Orbitrol valve, after the piston rod of the left cylinder has been fully projected and its piston is no longer able to yield, increases the pressure applied through pressure line 95 to the check valve 94 in the escape line from the piston end of the right cylinder. This enables the fluid applied to the rod end of said right cylinder to move the piston of said cylinder and eject the fluid contained in its piston end. As a result, the piston rod of the right cylinder begins to retract while the piston rod of the left cylinder remains locked in fully projected position, and the front wheels of the vehicle begin to turn to the right, and continue to turn to the right as long as the steering wheel of the Orbitrol valve is turned to the right, until they reach a rightwardly turned position symmetrically identical to the position illustrated in H6. 4C under conditions symmetrically identical to those described above when the hydraulic system was operated by means of the Orbitrol valve to turn the wheels of the vehicle to the left.

While I have described my invention with the aid of an exemplary embodiment thereof, it will be understood that the invention is not limited to the specific constructional details shown and described by way of example which may be departed from without departing from the spirit and scope of the invention.

[claim 1. An actuating arrangement for imparting predetermined different degrees of rotation to a pair of rotary bodies comprising means for mounting the rotary bodies for rotation about parallel axes; a pair of hydraulic cylinders having piston rods; means mounting said hydraulic cylinders for rotation about axes parallel to the axes of rotation of said rotary bodies; linkage means having ends arranged, upon shifting motion, to impart rotation to said rotary bodies; and means pivotally connecting the opposite ends of said linkage means and the free ends of both piston rods at a common location.

2. The arrangement according to claim 1 including hydraulic circuit means selectively operable to retract one of said piston rods while maintaining the other in projected position thereby causing a shifting and pivoting motion of said linkage means to rotate the rotary body adjacent the retracted piston rod through an arc, while the rotary body adjacent the projected piston rod is rotated in the same direction through an arc of lesser degree.

3. The arrangement according to claim 1 wherein said linkage means adjacent each rotary body comprise a first gear mounted upon said rotary body mounting means, a second gear in mesh with said first gear, an arm arranged to turn with said second gear, and a link pivotally connected to said arm.

4. The arrangement according to claim 1 wherein said linkage means adjacent each rotary body comprise a first gear mounted upon said rotary body mounting means for rotation therewith, a second gear of larger diameter than said first gear in mesh with said first gear, an arm extending diametrically across and arranged to turn with said second gear, said arm having an end projecting beyond the periphery of said second gear, and an adjustable link having an end pivotally secured to said projecting end of said arm.

5. Steering mechanism for vehicles comprising a pair of axially spaced wheels, means supporting said wheels for rotation about axes extending in a direction diametrically of said wheels, first gears carried by said wheel supporting means, second gears in mesh with said first gears, arms extending diametrically across and arranged to turn with said second gears and having ends projecting beyond the periphery of said second gears, a pair of hydraulic cylinders having piston rods projecting therefrom, means mounting said cylinders for rotation about axes parallel to the axes extending diametrically of the wheels at locations on opposite sides of the plane of symmetry of the wheels in their neutral positions, linkage means having ends pivotally connected to the projecting ends of said arms, means pivotally connecting the projecting ends of said piston rods and the opposite ends of said linkage means, and hydraulic circuit means for selectively retracting either one of said piston rods while maintaining the other one in projected position.

6. An actuating arrangement including first and second hydraulic cylinders having pistons and piston rods and hydraulic means for projecting the piston rod of said first cylinder from a retracted position while holding the piston rod of said second cylinder in fully projected position and for commencing retraction of the piston rod of said second cylinder after the piston rod of said first cylinder has reached its fully projected position, comprising a first fluid delivery line for delivering fluid under pressure into the piston end of said first cylinder, a second fluid delivery line for delivering fluid under pressure to the piston rod end of said second cylinder, means operable to supply metered amounts of fluid into said fluid delivery lines, a first fluid escape line at the piston rod end of said first cylinder, a second fluid escape line at the piston end of said second cylinder, first valve means arranged to block flow of fluid through said first escape line and adapted to open in response to a predetermined amount of pressure applied thereto, a pressure line leading from said fluid delivery lines to said first valve means to open said first valve means upon operation of said fluid supply means and thus enable the fluid delivered into said fluid delivery lines to advance the piston of said first cylinder, second valve means arranged to block flow of fluid thm ugh said second escape line, said second valve means being adapted to open in response to pressure of a higher order than required to open said first valve means, and a pressure line leading from said fluid delivery lines to said second valve means to open said second valve means when said fluid supply means is operated to deliver additional fluid into said fluid delivery lines after the piston rod of said first cylinder has reached its fully projected position and its piston is unable to yield further.

7. Arrangement according to claim 6 including a check valve in said fluid delivery lines.

8. An arrangement according to claim 6 wherein said hydraulic cylinders are mounted for rotation about parallel axes and the projecting ends of their piston rods are pivotally connected with each other.

9. A hydraulic actuating arrangement including first and second hydraulic cylinders having pistons and piston rods, means pivotally connecting the projecting ends of said piston rods, and hydraulic circuit means for retracting the piston rod of said first cylinder from a projected position while holding the piston rod of said second cylinder in a projected condition comprising first and second fluid delivery lines for delivering fluid to the piston rod end of said first cylinder and to the piston end of said second cylinder, respectively; first and second fluid escape lines at the piston end of said first cylinder and the piston rod end of said second cylinder, respectively; means operable to deliver metered amounts of fluid into said fluid delivery lines, first valve means in said first escape line arranged to block said line and adapted in response to a predetermined amount of pressure applied thereto to open said first escape line, a pressure line leading from said fluid delivery lines to said first valve means to open said valve means upon operation of said fluid delivery means, second valve means in said second fluid escape line arranged to block said line andadapted to open said second escape line in response to the application of pressure of a higher degree than required to open said first valve means; and a second pressure line leading from said fluid delivery lines to said second valve means to open said second valve means upon continued operation of said fluid delivery means after the piston rod of said first cylinder has been fully retracted.

10. A steering mechanism for turning a pair of steerable wheels from a spaced parallel relationship for straight ahead travel through different degrees of rotation about substantially vertical steering axes to follow separate curved paths about a common center point, said steering mechanism comprising: a pair of links pivotally connected together at one end; forming a knee-shaped joint with an included angle between links, and each link having an opposite end arranged to impart rotation to one of the steerable wheels; a pair of hydraulic cylinders mounted for pivotal movement about substantially vertical axes opposite the included angle between links and each hydraulic cylinder having a piston rod with a projecting end that is coupled with said pair of links at the knee-shaped joint; and hydraulic circuit means selectively operable to retract one of said piston rods while maintaining the other piston rod in projected position, thereby causing the knee-shaped joint to pivot about the hydraulic cylinder with a projected piston rod while moving towards the hydraulic cylinder with a retracted piston rod and at the same time straightening the knee-shaped joint to some extent for imparting rotation of different degrees to the steerable wheels.

ll. The steering mechanism described in claim 10 wherein said steerable wheels are centered in spaced parallel relationship for straight ahead travel when the piston rod of each hydraulic cylinder is fully extended in projected position, and control means for operating said hydraulic circuit means to fully extend both piston rods in projected positions for centering the steerable wheels. 

1. An actuating arrangement for imparting predetermined different degrees of rotation to a pair of rotary bodies comprising means for mounting the rotary bodies for rotation about parallel axes; a pair of hydraulic cylinders having piston rods; means mounting said hydraulic cylinders for rotation about axes parallel to the axes of rotation of said rotary bodies; linkage means having ends arranged, upon shIfting motion, to impart rotation to said rotary bodies; and means pivotally connecting the opposite ends of said linkage means and the free ends of both piston rods at a common location.
 2. The arrangement according to claim 1 including hydraulic circuit means selectively operable to retract one of said piston rods while maintaining the other in projected position thereby causing a shifting and pivoting motion of said linkage means to rotate the rotary body adjacent the retracted piston rod through an arc, while the rotary body adjacent the projected piston rod is rotated in the same direction through an arc of lesser degree.
 3. The arrangement according to claim 1 wherein said linkage means adjacent each rotary body comprise a first gear mounted upon said rotary body mounting means, a second gear in mesh with said first gear, an arm arranged to turn with said second gear, and a link pivotally connected to said arm.
 4. The arrangement according to claim 1 wherein said linkage means adjacent each rotary body comprise a first gear mounted upon said rotary body mounting means for rotation therewith, a second gear of larger diameter than said first gear in mesh with said first gear, an arm extending diametrically across and arranged to turn with said second gear, said arm having an end projecting beyond the periphery of said second gear, and an adjustable link having an end pivotally secured to said projecting end of said arm.
 5. Steering mechanism for vehicles comprising a pair of axially spaced wheels, means supporting said wheels for rotation about axes extending in a direction diametrically of said wheels, first gears carried by said wheel supporting means, second gears in mesh with said first gears, arms extending diametrically across and arranged to turn with said second gears and having ends projecting beyond the periphery of said second gears, a pair of hydraulic cylinders having piston rods projecting therefrom, means mounting said cylinders for rotation about axes parallel to the axes extending diametrically of the wheels at locations on opposite sides of the plane of symmetry of the wheels in their neutral positions, linkage means having ends pivotally connected to the projecting ends of said arms, means pivotally connecting the projecting ends of said piston rods and the opposite ends of said linkage means, and hydraulic circuit means for selectively retracting either one of said piston rods while maintaining the other one in projected position.
 6. An actuating arrangement including first and second hydraulic cylinders having pistons and piston rods and hydraulic means for projecting the piston rod of said first cylinder from a retracted position while holding the piston rod of said second cylinder in fully projected position and for commencing retraction of the piston rod of said second cylinder after the piston rod of said first cylinder has reached its fully projected position, comprising a first fluid delivery line for delivering fluid under pressure into the piston end of said first cylinder, a second fluid delivery line for delivering fluid under pressure to the piston rod end of said second cylinder, means operable to supply metered amounts of fluid into said fluid delivery lines, a first fluid escape line at the piston rod end of said first cylinder, a second fluid escape line at the piston end of said second cylinder, first valve means arranged to block flow of fluid through said first escape line and adapted to open in response to a predetermined amount of pressure applied thereto, a pressure line leading from said fluid delivery lines to said first valve means to open said first valve means upon operation of said fluid supply means and thus enable the fluid delivered into said fluid delivery lines to advance the piston of said first cylinder, second valve means arranged to block flow of fluid through said second escape line, said second valve means being adapted to open in response to pressure of a higher order than required tO open said first valve means, and a pressure line leading from said fluid delivery lines to said second valve means to open said second valve means when said fluid supply means is operated to deliver additional fluid into said fluid delivery lines after the piston rod of said first cylinder has reached its fully projected position and its piston is unable to yield further.
 7. Arrangement according to claim 6 including a check valve in said fluid delivery lines.
 8. An arrangement according to claim 6 wherein said hydraulic cylinders are mounted for rotation about parallel axes and the projecting ends of their piston rods are pivotally connected with each other.
 9. A hydraulic actuating arrangement including first and second hydraulic cylinders having pistons and piston rods, means pivotally connecting the projecting ends of said piston rods, and hydraulic circuit means for retracting the piston rod of said first cylinder from a projected position while holding the piston rod of said second cylinder in a projected condition comprising first and second fluid delivery lines for delivering fluid to the piston rod end of said first cylinder and to the piston end of said second cylinder, respectively; first and second fluid escape lines at the piston end of said first cylinder and the piston rod end of said second cylinder, respectively; means operable to deliver metered amounts of fluid into said fluid delivery lines, first valve means in said first escape line arranged to block said line and adapted in response to a predetermined amount of pressure applied thereto to open said first escape line, a pressure line leading from said fluid delivery lines to said first valve means to open said valve means upon operation of said fluid delivery means, second valve means in said second fluid escape line arranged to block said line and adapted to open said second escape line in response to the application of pressure of a higher degree than required to open said first valve means; and a second pressure line leading from said fluid delivery lines to said second valve means to open said second valve means upon continued operation of said fluid delivery means after the piston rod of said first cylinder has been fully retracted.
 10. A steering mechanism for turning a pair of steerable wheels from a spaced parallel relationship for straight ahead travel through different degrees of rotation about substantially vertical steering axes to follow separate curved paths about a common center point, said steering mechanism comprising: a pair of links pivotally connected together at one end, forming a knee-shaped joint with an included angle between links, and each link having an opposite end arranged to impart rotation to one of the steerable wheels; a pair of hydraulic cylinders mounted for pivotal movement about substantially vertical axes opposite the included angle between links and each hydraulic cylinder having a piston rod with a projecting end that is coupled with said pair of links at the knee-shaped joint; and hydraulic circuit means selectively operable to retract one of said piston rods while maintaining the other piston rod in projected position, thereby causing the knee-shaped joint to pivot about the hydraulic cylinder with a projected piston rod while moving towards the hydraulic cylinder with a retracted piston rod and at the same time straightening the knee-shaped joint to some extent for imparting rotation of different degrees to the steerable wheels.
 11. The steering mechanism described in claim 10 wherein said steerable wheels are centered in spaced parallel relationship for straight ahead travel when the piston rod of each hydraulic cylinder is fully extended in projected position, and control means for operating said hydraulic circuit means to fully extend both piston rods in projected positions for centering the steerable wheels. 